GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC B3128 Driver Door Unlock CKT Short to B+

Object Number: 385149 Size: LF

Circuit Description

The driver door unlock circuit is completed by the BCM when it receives a driver door unlock request from any of the door lock switches, or the keyless entry transmitter. The BCM momentarily grounds circuit 1391, energizing the door lock relay.

Conditions for Setting the DTC
    • The BCM detects a short to B+ in circuit 1391 while attempting to ground circuit 1391.
    • The BCM tests for a short to B+ in circuit 1391 only when attempting to unlock the driver's door.
    • All conditions must be present for more than 0.15 seconds.

Action Taken When the DTC Sets
    • The BCM stores DTC B3128 in memory.
    • The BCM turns off its output to the door lock relay.

Conditions for Clearing the DTC
    • When the ignition switch is cycled form off to on, the current DTC is cleared. If the fault is present at the next unlock activation, this DTC sets as current.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • Using a scan tool.

Diagnostic Aids
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent short to B+ in circuit 1391.
       - The BCM is shorted to B+ internally.
       - The door lock relay coil is shorted to B+ internally.
    • If the DTC is a history DTC, the problem may be intermittent. Try performing the tests shown while moving wiring and connectors, this can often cause the malfunction to reappear.
    • DTC P1626 will set in the Powertrain Control Module (PCM) when the ignition switch is on with the Body Control module (BCM) disconnected. When BCM diagnostics and repairs are completed, refer to Engine Controls for additional information on PCM related DTCs.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step checks for a short to B+ in circuit 1391.

    2.

  2. This step determines whether circuit 1391 has a short to B+ or the BCM is faulty.

    3.

  3. This step checks BCM DTC B3128 and checks for BCM DTC B3128 to set again.

Step

Action

Value(s)

Yes

No

1

Was the BCM Diagnostic System Check performed?

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Go to Step 2

Go to Diagnostic System Check - Body Control System

2

  1. Disconnect the door lock relay connector.
  2. Using a test lamp, connect between the door lock harness connector terminal C2 and ground.

Is the test lamp on?

--

Go to Step 3

Go to Step 4

3

  1. Leave the test light in the same location from the previous step.
  2. Turn the ignition switch to the LOCK position.
  3. Disconnect the BCM connectors.
  4. Turn the ignition switch to the RUN position.

Is the test lamp on?

--

Go to Step 5

Go to Step 6

4

Replace the door lock relay.

Is the repair complete?

--

Go to Step 9

--

5

Repair short to B+ in circuit 1391.

Is the repair complete?

--

Go to Step 9

--

6

  1. Turn the ignition switch to the LOCK position.
  2. Reinstall connectors/components removed.
  3. Turn the ignition switch to the RUN position.
  4. Clear BCM DTCs. Refer to Clearing DTCs for more information.
  5. Press unlock on either door lock switch.
  6. Check for BCM DTCs. Refer to Diagnostic Trouble Code (DTC) Displaying for more information.

Does BCM DTC B3128 reset as a current DTC?

--

Go to Step 7

Go to Step 8

7
  1. Replace the BCM. Refer to Body Control Module Replacement for more information.
  2. After replacing the BCM, perform the Setup New BCM procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration for more information.

Is the repair complete?

--

Go to Step 9

--

8

The malfunction is not present at this time. Refer to Diagnostic Aids for additional information regarding this DTC.

--

--

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9
  1. Turn the ignition switch to the LOCK position.
  2. Reinstall connectors/components removed.
  3. Turn the ignition switch to the RUN position.
  4. Clear BCM DTCs. Refer to Clearing DTCs for more information.
  5. Check for BCM DTCs. Refer to Diagnostic Trouble Code (DTC) Displaying for more information.

Are there any BCM current DTCs set?

--

Go to Diagnostic System Check - Body Control System

System OK